Electronic devices typically include a computing engine, a display, and an interactive device responsive to the input of a user. For example, a computer may include a computing circuit, a CRT for display, and a keyboard and mouse responsive to a user's input. As a second example, a Personal Digital Assistant includes a computing circuit, an LCD display, and a touch screen formed over the LCD display, together with some buttons. Many electronic devices, in particular mobile devices, miniature devices, devices that require a re-programmable interface, or devices that require a robust and simple user interaction mechanism rely upon touch screens placed over a display to provide user interaction capabilities to the device.
There are many touch screen technologies such as resistive wire, acoustic, and infra-red. These are generally placed above either a CRT screen or LCD screen to provide the required interactive functionality in a single component composed of two parts. Typically, the display (for example, LCD or CRT) is manufactured while the touch screen is made separately. After the display and touch screen are manufactured, they are integrated in a common housing to provide a single component that can be built into a complete electronic device.
Resistive wire touch screens are built upon a substrate that is coated with a resistive film, typically indium tin oxide (ITO) at a specified thickness, uniformity and resistivity. Other resistive touch screen materials, such as spacer dots, conductive films, etc., are carefully formed upon the coated substrate to create a resistive touch screen. When conventionally combined with a display, the multi-layer component has inferior optical characteristics to the display device alone due to inter-layer reflections, has redundant manufacturing steps, and redundant components. Moreover, the additional step of integrating the components raises manufacturing costs for the complete device. The manufacturing processes for display-and-touch-screen devices are well known in the art and products are available today from a variety of vendors. For example, U.S. Pat. No. 5,795,430 issued Aug. 18, 1998 to Beeteson et al., describes an adhesive material dispensed onto a faceplate and used to attach a touch screen.
A new class of display devices based upon organic light-emitting diodes (OLEDs) is formed by depositing patterned conductive and organic materials upon a substrate. This substrate can be identical to the substrate used for resistive wire touch screens. Moreover, the materials used for the patterned conductive materials are similar to, or the same as, those used for the resistive films, but their uniformity, thickness and resistivity may vary. The OLED displays are made by patterning a conductive material that is formed on a substrate. For an OLED display, the conductive material is ideally a low resistivity film, whereas for a touch screen substrate a controlled higher resistivity film is employed. If an active-matrix display device is desired, electronic components such as transistors and capacitors are also formed on the patterned conductive material in a desired circuit design. Once the conductive pattern and electronic components are formed, organic materials are deposited, followed by any remaining conductive elements, planarization layers, and other layers as known in the prior art. The organic materials are sensitive to and degraded by moisture, heat, and ultra-violet radiation. Connecting pads are defined as part of the conducting pattern and are wire-bonded to a cable after the device is encapsulated. The process by which the OLED display device is made uses well-known photolithographic, deposition, bonding, and encapsulation methods commonplace in the integrated circuit industry.
However, a problem exists with the conventional practice of forming separate OLED displays and touch screens and then combining them, in that the additional layers in the touch screen reduce the brightness of the display, reduces the optical quality of the display due to additional internal reflections from the layers of the touch screen, and add cost due to the need for two substrates and a complex housing for the two elements. U.S. Pat. No. 6,424,094 B1 issued Jul. 23, 2002 to Feldman addresses this problem for a bottom-emitter OLED display (one viewed through the substrate) but the proposed solution may not be applicable to a top-emitter display (one viewed through the cover).
Although epoxy adhesives are used for bonding covers to substrates, methods of adhesive application are problematic for use with OLED materials since commonly-used epoxies require either ultra-violet radiation and/or heat to cure, both of which can degrade the organic materials in the OLED display. Moreover, a conventional application of adhesive material and curing as taught, for example, in U.S. Pat. No. 5,795,430 (cited above) is problematic in that the circuit elements including silver inks used on the edges of resistive-wire touch screens obscure the adhesive material beneath the inks. Adhesives are known that cure in shadowed areas not directly exposed to curing radiation, for example Appli-Tec 6202, but these require a secondary heating process to complete the cure that can destroy the OLED materials. Other known adhesives that are not light curable lack the necessary properties required to form a hermetic seal for the OLED materials, or require excessive heat for curing.
Other types of touch screens, such as those employing surface acoustic wave, capacitive and inductive technologies also include light blocking circuit elements that extend to the edges of the touch screen and may obscure the light curing of a light curing adhesive material.
There is a need therefore for an improved integrated resistive touch screen and top-emitter OLED display that reduces redundant components in the devices, reduces cost, improves optical qualities, and is more robust and a manufacturing method therefore.